I have a 2003 Suzuki Z400 that hasn't been ran in a year. I have changed the old stale fuel out with fresh, I have completely disassembled the carb and cleaned it out, but it still back fires anytime it is running, except at an idle. If you ride at a steady pace it backfires, if you blip the throttle, it backfires. When you hold it wide open it REALLY backfires. The only mods to the bike are a k&n filter, and a FMF Ti-4 with a powerbomb headpipe. It is currently jetted with a 60 pilot 3.5 turns on the air screw, and a 150 main. I don't know where the needle is at. Any help on this problem would be appreciated.

Thanks

 

did you change the spark plug too?whats the plug look like ?white flaking on it .sound like your running lean go up to a 155 or 160 main .

 

You might need to adjust your valves.

 

Definetly sounds lean. If you pull on the choke..does the back firing stop?

 

Check for possiable air leaks in your airintake from your air filter to the engine, some times the intake tubes can slighty come off the if the clamps comes loose or jared